1. Field of the Invention
The present invention relates to a video output apparatus which outputs one of image information items received from external storage units.
2. Description of the Related Art
To project an image by a projector, a video signal is input to the projector from a computer. Some projectors may have a plurality of input interfaces (I/F). For example, input interfaces to which image cables are connected, such as D-Sub, HDMI, and DisplayPort, are known. In the following, the input of a video signal by the image cable is called cable input. The projector of this type only includes a single projection lens and a single optical engine and has to select one of the plurality of input interfaces to which video signals are input as an input interface of a video signal for projection. If the input interface connected to an image cable to which the video signal for projection is input changes, the projector has to switch the input interface to the input interface of the video signal for projection.
For example, a case in which a projector and a computer are connected by a RGB cable of a D-Sub connector to project an image by the projector is considered. In this case, it is necessary to connect the RGB cable from the computer to the projector and switch the input interface used for projection by the projector to the D-Sub interface. In a method of performing switching of video-signal inputs according to the related art, the switching of video-signal inputs is performed by a user's key operation on a body portion of the projector or a remote controller of the projector.
Moreover, a method of performing the switching of the video signals according to the cable input automatically is also known in the art. In this method, a computer and a projector are connected by a cable and when the projector detects reception of a video signal from the outside and determines the presence of the video signal, the switching of the video signals is performed.
Furthermore, a method of performing the switching of the input interfaces according to the cable input is also known in the art. In this method, the presence of the video signals by the cable input is checked sequentially according to the switching order of the input terminals.
For example, Japanese Laid-Open Patent Publication No. 2001-255861 discloses an automatic switching method. In this method, when a switching request to a next input terminal is received from an input device, the switching order of the input terminals stored in a storage part is retrieved. A second retrieval part checks whether an input signal is present in a signal input state information corresponding to the next input terminal based on the retrieved input terminal information. When the input signal is present in the information, a switching process to switch the present input terminal to the next input terminal is performed.
In recent years, projectors may project an image file or a motion picture file received from a network and may project an image file or a motion picture file stored in an external storage, such as a USB memory. In the following, the input of a video signal by the image file or the motion picture file is called file input.
For example, a projector and a server may be connected via a network and an image of the content (an image file, a motion picture file, etc.) stored in the server may be projected by the projector. In the following, the projection of the image in this way is called server projection. Moreover, an external storage may be connected to a projector and an image of the content stored in the external storage may be projected by the projector. In the following, the projection of the image in this way is called external storage projection.
Therefore, it is necessary for a projector including a plurality of input interfaces according to the file input to perform the switching of the input interfaces.
In a case of the file input, the projector according to the related art simply determines presence of a video signal when a user operates the projector to switch the input of the video signal to the file input. If the user manually switches the input of the video signal to the server projection, the projector according to the related art simply determines the presence of the video signal of the server projection. Moreover, the projector according to the related art simply determines presence of a video signal when connection between the projector and an external storage is established. For example, if the projector detects connection of an external storage to the projector, the projector according to the related art simply determines the presence of an image file for projection.
As described above, the switching method of performing switching of the input interfaces by the file input according to the related art simply determines whether a user's operation is performed on the projector, or determines whether an external storage is connected to the projector. However, this is insufficient for determining whether an image of the content in the server or the external storage may be properly projected by the projector. In other words, there may be a case in which even if the user operates the projector to switch the image input to the server projection, the projector is not connected to the server via the network. There may be also a case in which even if the projector detects connection of an external storage to the projector, a file system of the content in the external storage is damaged and an image file may not be read from the external storage. Therefore, even if an image file may not be read from the server or the external storage and an image of the content may not be properly projected, the switching method according to the related art determines the presence of the video signal. In such a case, the switching of the input interfaces may not be performed appropriately.